1. Field of the Invention
The present invention relates to a method for adjusting and evaluating a light intensity distribution of an illumination apparatus, an illumination apparatus, an exposure apparatus, and a device manufacturing method.
2. Description of the Related Art
In a projection exposure apparatus configured to manufacture semiconductor devices, a light flux is emitted onto a pattern-formed reticle from an illumination optical system and the pattern is projected and exposed on a wafer by a projection optical system. Numerical aperture (NA) and lighting conditions of the projection optical system are optimized in manufacturing a semiconductor device having a finer pattern. The lighting conditions are determined by a coherence factor (σ value=NA of the illumination optical system divided by NA of the projection optical system).
In the illumination optical system of the projection exposure apparatus, a relation of a secondary light source image formed by an optical integrator that is located in the illumination optical system to a surface to be illuminated corresponds to a relation of a pupil to the surface to be illuminated. Thus, the NA of the illumination optical system can be adjusted by changing the size of the secondary light source in the illumination optical system.
Further, Japanese Patent Application Laid-Open No. 5-283317 and Japanese Patent Application Laid-Open No. 2001-033875 discuss an illumination apparatus and an exposure apparatus capable of improving focal depth and resolution. Conventionally, according to the aforementioned apparatuses, an optimum secondary light source having various shapes of light distribution can be formed. Such shapes are, for example, an annular shape (a ring-like shape), a quadrupolar shape, etc.
If a light intensity distribution of a secondary light source formed on a pupil plane in the illumination optical system is substantially uniform, in other words, if the light intensity of the secondary light source is substantially uniform in the light distribution area, it is easy to grasp a relation between the size or shape of the light intensity distribution and imaging characteristics. However, the light intensity distribution of the secondary light source of the exposure apparatus is actually not uniform, and comparatively significant nonuniformity is seen in the intensity distribution.
Conventionally, only an outer shape, for example, positions where a cumulative light quantity distribution in the radial direction is 10% or 90% (σ 10%, σ 90%) of the total quantity of light are considered in an evaluation of a light intensity distribution regardless of nonuniformity of the light intensity distribution. However, even if light intensity distributions agree in positions of σ 10% and σ 90%, a difference in nonuniformity of the light intensity distribution may produce a difference in imaging performance. Thus, conventionally, imaging characteristics cannot be correctly evaluated based on the size and shape of a light intensity distribution and, for example, a variation in line width resolution may occur between different exposure apparatuses.
Further, in order to eliminate this inconvenience, the illumination apparatus and the exposure apparatus have to be repeatedly fine-controlled using an actual pattern.
On the other hand, there is known a simulation technique used for determining optimum lighting conditions for a reticle. However, in order to set a secondary light source equivalent to the lighting conditions acquired by the simulation in the exposure apparatus, for the same reason, the illumination apparatus and the exposure apparatus need to be fine-controlled using an actual pattern.